Local Path Planning For Underwater Gliders Using Artificial Potential Field Approach

Underwater glider is a kind of underwater vehicles driven by its own net buoyancy.Because of its characteristics of less energy consumption,longer distance and better concealment,it has attracted more and more attention in recent years.As underwater vehicle technology advances,people's requirements for smart underwater glider are getting demanding.Path planning is important in autonomy improvement for underwater robots.It is also a prerequisite for successful task accomplishment.For underwater glider path planning,one of the most basic and the most important requirements is to ensure safety.Therefore,achieving a collision-free path is an essential part in underwater glider control.This has been attracting people's attention since the concept of underwater glider was brought forth.Path planning for underwater gliders involves two parts: global waypoint setting and local underwater path planning.For underwater gliders operating in an unknown ocean,it is quite possible that the vehicle gets damaged or even lost by colliding with underwater obstacles.This thesis focuses on local path planning for underwater gliders.A path planning approach is developed by constructing artificial potential fields(APFs)between the underwater glider and the environment,and taking the underwater glider's motion kinematic parameters as motion constraints.The main contributions and achievements are summarized as follows:(1)In current ocean observations,when the underwater glider encounters obstacles near the sub-goal area,the usual action is to stop the observation as in an emergency.Such strategies will evitable lead to an incomplete data collection.To avoid such problem,an APF-based path planning approach is applied to generate a collision-free path for underwater glider as it travels in the water.Modified APFs are constructed between the underwater glider and the marine environment.(2)The underwater glider's motion ability is to some extent limited by its design and physical structure.Ignorance of it motion restraints in local path planning may lead to generation of an infeasible path that the underwater glider could not follow.Therefore,in the presented approach,the underwater glider's motion constraints are embedded in local path generation.The kinematic parameters used to represent the motion constraints include gliding angle and turning radius.(3)Turning motion of the underwater glider is realized by adjusting the internal attitude adjusting slider.In order to enable the underwater glider to follow the path planning result and make a turn with a practical radius,dynamic model is used to establish a mapping between the virtual centripetal force resulted from the constructed APFs and the actual centripetal force acted on the underwater glider.The relation between turning radius and rotation angle of the attitude adjusting slider is also deduced.Accordingly,the turning radius can be calculated for a specific rotation angle of the attitude adjusting slider.The relation between the two parameters is of great significance and provides guidance for controlling turning motion of the underwater glider.